The goal of this proposal is to study the effect of sympathetic innervation on the formation of 21 and 22 adrenoceptor (AR) signaling complexes in the heart. We will investigate how these complexes either facilitate or restrict receptor signaling;we will identify the structural domains of the receptors that are needed for interaction with the other components of the signaling complex;and we will identify cellular proteins that define these subtype-specific signaling complexes. 21ARs and 22ARs are prototypical G protein coupled receptors (GPCRs), the largest family of hormone and neurotransmitter receptors in the human genome. These receptors are essential for the physiologic regulation of cardiac function in response to catecholamines (adrenaline and noradrenaline) released from sympathetic nerves. Recent studies suggest that 21ARs and 22ARs play distinct roles in the pathogenesis of heart failure, a growing health problem in the United States. We have developed an experimental system to study the important interface between sympathetic nerves and the heart using co-cultures of neonatal cardiac myocytes and sympathetic neurons. Our preliminary studies show that 21ARs and 22ARs have differential subcellular targeting relative to these synapses, and that signaling complexes form at the sites of synapse formation. The following aims are designed to characterize these signaling complexes. Aim 1. Determine the structural basis for subtype specific targeting and trafficking of 21ARs and 22ARs in cardiac myocytes. Aim 2. Determine the functional significance of subtype-specific localization of 21ARs and 22ARs relative to sympathetic synapses. Aim 3. Characterize protein components of the 21AR and 22AR signaling complexes in cardiac myocytes innervated by sympathetic neurons. Aim 4. Determine the functional significance of interacting proteins identified in Aim 3 on 21AR and 22AR signaling and trafficking in cardiac myocytes, and verify their existence in signaling complexes in the adult heart. The proposed studies will provide new information about how the brain regulates heart function. We will characterize the mechanism by which noradrenaline and adrenaline released from sympathetic nerves alters heart function by activation of two specific adrenergic receptors. This research will further our understanding of the development of diseases such as heart failure and sudden death.